1. Field of the Invention
The present invention relates to a thin micro reformer used in a fuel cell system. More particularly, the invention relates to a thin micro reformer which has a channel extended from a fuel inlet portion, along a periphery of a substrate to allow the fuel to flow therethrough to be preheated and enable heat exchange in a reformer and a CO remover, thereby significantly improving heat efficiency and enabling reformation of the fuel and removal of CO in a single sheet of substrate.
2. Description of the Related Art
Recently, there have been increased uses of portable small-sized electronic devices including mobile phones, Personal Digital Assistants (PDAs), digital cameras, notebook computers and the like. In particular, since the launch of Digital Multimedia Broadcasting (DMB) through the mobile phones, the portable small-sized terminals are required to have increased power capacity. Lithium ion secondary batteries used in general to date, which have capacity for two-hour viewing of DMB, are undergoing efforts to improve its capacity, but there have been growing expectations on small-sized fuel cells for a more fundamental solution.
In order to realize such a small-sized fuel cell, either a direct methanol method in which methanol is directly supplied to a fuel electrode or a reformed hydrogen fuel cell (RHFC) method in which hydrogen is extracted from methanol and supplied to a fuel electrode can be adopted. The RHFC method uses hydrogen as fuel as in Polymer Electrode Membrane (PEM) method, thus having advantages in terms of output, power capacity per volume and in that it requires no reactants besides water. However, the method requires a reformer, thus having a disadvantage for miniaturization.
In order for the fuel cell system to obtain high power output density, a reformer is required to convert liquid fuel into gaseous fuel such as hydrogen gas. The reformer includes an evaporating part for gasifying methanol, a reforming part for converting methanol into hydrogen via catalytic reaction at a temperature from 250° C. to 290° C., and a CO removing part for removing CO, a by product. In the reforming part, heat absorption reaction takes place and the temperature should be maintained from 250° C. to 290° C. Also in the CO removing part, the temperature should be maintained at about 170° C. to 200° C. to allow effective reaction.
As a conventional example, Japanese Patent Application Publication No. 2004-288573 discloses a small-sized reforming apparatus 250 as shown in FIG. 1. Such a conventional small-sized reforming apparatus 250 includes an insulation package 258, and includes a fuel evaporator 251 for combustion, a fuel evaporator 255 for power generation, a first combustor 252, a CO remover 257, a second combustor 254, a reformer 256 and a third combustor 253 which are stacked sequentially in the insulation package 258.
At the bottom of the fuel evaporator 251 for combustion, insulation supporting members 261 and 262 are disposed. These insulation supporting members 261 and 262 support and allow the fuel evaporator 251 for combustion to be disposed apart from an inner wall of the insulation package 258. Such a conventional reforming apparatus has a multilayer structure of at least 10 layers, which makes it difficult to achieve miniaturization.
That is, even if each layer is thin, the overall structure is inevitably thick in its volume and the difficulty in bonding the multiple layers hinders mass-production.
In the meantime, EP No. 0991465 discloses a conventional reformer 300 having multiple layers, which adopts the heat exchange method as shown in FIG. 2. This reformer 300 includes a reaction chamber 320 disposed above a heat exchange chamber 314 with an emission chamber 322 disposed therebetween, thereby forming a stacked structure.
In this reformer 300, the heat is exchanged through multiple layers consisting of the reaction chamber 320, the heat exchange chamber 314 and the emission chamber 322. The reaction chamber 320 provides a channel for heat generation reaction where the heat generated via heat generation reaction is used for heat absorption reaction. The heat exchange member 314 provides a channel where the heat generation is terminated and the heat is exchanged. This method allows heat exchange but increases overall thickness and exhausts fuel, hindering heat efficiency.
FIG. 3 illustrates another conventional reformer 400, in which a fuel inlet 410 and a gassifier 420 with a heater 422 are disposed at a side of a substrate 410. Downstream of the fuel inlet 410 and the gassifier 420, a reformer 430 and a CO remover 440 are disposed. Downstream of the CO remover 440, a hydrogen outlet 442 is disposed. Such a conventional reformer, however, uses a heater 422 to heat up the fuel, consuming a great amount of energy.
In addition, the conventional method yields a large volume with difficult manufacturing processes. Further, using a silicon substrate and glass, which has high heat conductivity, the method does not facilitate the optimal reaction temperature distribution which requires at least 250° C. maintained in the reforming part, and 190° C. maintained in the CO removing part.
Therefore, there exists a need in the art for a reformer having a thin structure where fuel is reformed and CO is removed in a single sheet of substrate, improved in capacity with high heat efficiency without consuming much energy.